This invention relates to a fluid displacement apparatus, and more particularly, to improved scrolls for a scroll type fluid displacement apparatus.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 to Cruex discloses the basic construction of a scroll type apparatus. The scroll type apparatus includes two scroll members each having a circular end plate and spiroidal or involute spiral element. These scroll members are maintained at an angular and radial offset so that the spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surfaces and, therefore, the fluid pockets change in volume. Since the volume of the fluid pockets increases or decreases, depending on the direction of the orbital motion, the scroll type fluid apparatus is applicable to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type, a scroll type fluid displacement apparatus has some advantages such as fewer parts, continuous compression of fluid and others. However, there have been several problems with such scroll type fluid displacement apparatus, including ineffective sealing of the fluid pockets and wearing of the scroll members.
Generally, in scroll type fluid displacement apparatus, the scroll members are formed of aluminum or an aluminum alloy to reduce the weight of the apparatus. The surface of the spiral element of the orbiting scroll member also can be treated with alumite because, if the contact surface between the spiral elements grounds the aluminum, abnormal wear or mechanical loss is caused by the cohesive force between the aluminum surfaces. An oxidizing film of aluminum on the orbiting scroll reduces the cohesive force and provides a smoother operation. However, because the surfaces of the scroll members usually are finished by end milling, the aluminum surface is rough. Even if the rough surface of one or both of these scroll members is treated with alumite, the rough alumite treated surface is in contact with the aluminum surface of the other spiral element which causes abnormal wear of the spiral elements.